1. Field of the Invention
The present invention provides a method for inspecting transparent containers for refractive defects and associated apparatus. More specifically, the invention provide:s for a multiple intensity gradient light grid filter which converts light emitted by a diffuse light beam into a light gradient which impinges upon a transparent container with a detector receiving light passing through the container and emitting responsive electrical signals to a processor which determines whether a refractive defect exists in the container.
2. Description of the Prior Art
It has long been known to inspect various properties of transparent containers by passing a light beam through the container and having detectors receive the light passing therethrough, convert the light into corresponding electrical signals and deliver the signal to a suitably programmed processor which compares the received signal with a stored standard in order to determine a given characteristic of the container.
U.S. Pat. No. 4,924,083 discloses a method and apparatus for inspecting a sidewall of a bottle wherein a moving slit is synchronized with the detection means to introduce a gradient in the light source to enhance the view of refractive defects. The nature of this system, however, imposes a meaningful limitation on speed of inspection, enhances only horizontal edges of the container and provides a system which would require substantial maintenance.
U.S. Pat. No. 4,610,542 discloses a system wherein a single linear lamp is positioned behind and at the top of the diffuser. This causes the diffuser to emit more light in the upper portion than at the bottom with a smooth gradient from light to dark in between. A lens positioned near the diffuser collimates the light in order that different intensities are projected in different directions with a smooth gradation from top to bottom. This system is disclosed as only viewing the front wall of the container. This system is designed to be insensitive to small cosmetic type defects and large gentle thickness variations such as settle waves which may occur on the inside of the container wall, for example.
U.S. Pat. Nos. 4,487,322 and 4,601,395 disclose placing a filter over a diffuse light source which backlights the container to provide a single intensity gradient of light to dark parallel to the container""s longitudinal axis. A lens is said to focus the light from a narrow vertical area on the front surface of the container onto a plurality of sensors arranged in the vertical column. The recorded intensity of the adjacent detectors is then compared with a bottle which passes inspection. The variation would be equal from detector to detector. This system, however, examines only the front wall of the container. It also requires that the container be axially rotated in order to inspect 360xc2x0 of the sidewall. Such rotation limits inspection speed as well as requiring additional maintenance. The system is intended primarily to detect horizontally oriented transparent defects, such as ribbon tears, for example. These are large horizontal defects that are structurally hazardous.
U.S. Pat. No. 4,601,395 also discloses a filter composed of transversely spaced outer zones of substantially uniform illumination intensity and a third central zone between first and second zones in which the intensity of the diffused illumination is different from the intensities of the outer zones. These systems are designed primarily to enhance gross defects such as ribbon tears and the like which compromise the strength of the container, but are not designed to also detect cosmetic defects in the container.
U.S. Pat. No. 5,004,909 discloses alternating in black and white stripes in a diffuse light source to enhance the view of refractive defects. The containers must be rotated in order to achieve inspection of the full sidewall. A simple comparison of light levels on three adjacent sensing elements is employed to detect the refractive index. The gradient produced by the solid black to solid white stripes results in a complex image as it enhances the normal non-defect thickness variations in addition to refractive defects. As a result, it lacks the capability of efficient sorting between defects and non-defects in normal container production.
U.S. Pat. No. 5,216,481 discloses alternating black and white stripes of diffuse light source to enhance the view of refractive defects. A two-dimensional detecting means is employed and multiple inspection zones are provided to establish circumferential inspection coverage.
In spite of the foregoing disclosures, there is lacking an effective method and associated apparatus for effecting efficient inspection of transparent containers such that refractive defects including minor defects can be detected in an automated, rapid, accurate fashion while avoiding rejections based upon purposeful features, such as detection of desired regions which lack wall uniformity.
The present invention has met the hereinbefore-described needs.
The method of the present invention includes inspection of a transparent container, such as a glass container, for refractive defects by positioning the container between a light source and a detector, passing diffused light from the light source through a grid filter which establishes multiple intensity gradient bands which impinge on and inspect both the front and rear container walls for refractive defects which may be structural in nature or cosmetic in nature. The grid filtered multiple intensity gradient light passes through the container walls and is received by a detector which converts the light received into responsive electrical signals which are delivered to a processor which determines whether a refractive defect exists.
The method of the present invention does not require axial rotation of the container and preferably has the light and dark bands of the grid filter being alternated with each having light transmission properties of about 1 to 80%. The processor also avoids rejection of the container based upon desired or purposeful irregularities in the container wall.
The apparatus of the present invention provides a diffuse light source, a grid filter which preferably has a plurality of alternating light and dark bands which provide intensity gradients throughout the field of view with a lens directing the grid filtered light through the transparent container wall of the container being inspected. The light passing through container walls which do not have a refractive defect either of a structural or objectionable cosmetic variety will provide predetermined light impinging on the detector which in turn converts the light into corresponding electrical signals. The processor which may be any suitably programmed computer having stored information regarding the nature of defects which will result in rejection of the container, and preferably the irregularities in the container wall which are deemed acceptable, will effect a comparison between the electrical signals and the information and make a determination as to whether the container is rejected.
It is an object of the present invention to provide a method and associated apparatus for efficiently and rapidly inspecting transparent containers for refractive defects.
It is a further object of the present invention to provide such a method and apparatus which will not only determine the presence of refractive defects which provide a structural problem, but also those which provide a meaningful cosmetic problem.
It is a further object of the present invention to provide such a system which will, in processing information, distinguish between refractive defects and desired irregularities in a portion of a container wall.
It is yet another object of the present invention to provide such an inspection system which will effect inspection without requiring axial container rotation.
It is a further object of the present invention to provide such a system which makes shallow defects visible, while permitting inspection of a large field of view.
It is yet another object of the present invention to provide such a system which inspects both the front wall and rear wall of a container at substantially the same time.
It is another object of the present invention to provide such a system which employs a triangular wave having a constant absolute slope.
It is yet another object of the present invention to provide a system for determining the presence of horizontal and oblique cosmetic refractive defects which are of a subtle nature.
These and other objects of the invention will be more fully understood from the following detailed description of the invention on reference of the illustrations appended hereto.